Mother can file a suit for partition and possession of the proeprty along with an application for interim stay pending the suit if the property was ancestral and she has share by intestate succession.

1) mother should file suit for partition for division of property by metes and bounds 

2) seek injunction restraining sale of property 

1. If your grand father from mother's side has died after 2005 the only your mother has share in the ancestral of her father. Otherwise not unless the property left by her father is self acquired.

2. Considering that she has share in the property she can file a suit for partition and injunction so during the pendency of the case the joint property may not be sold by her brothers.

3. this is the only way to get her due share unless her brothers agrees for settlement and give her share. 

File partition suit, she has equal share along with brothers. Court will grant stay on sale and against alienation of property in any manner.

A civil suit mustvbe filed seeking temporary injunction against any heirs selling the property. Also a partition suit must also be filed in the city civil court.

Regards 

By sending proper legal notice to brothers and party that she has her share in the ancestral property as per the Indian Succession Act.

They can't sell it without her consent. Your sister can file partition suit along with stay for not selling the said property and creation of third party rights by brothers

1.  Mother can obtain a "restraining order" from the local Civil Court, restraining the brothers from selling the property.

2. File caveat with the registering authority and the tahsil office restraining them from making any further transfers of the property till Mother is heard and taken on record.

Get issued a notice in local news papers where the property is situated restraining public from dealing with the property.

Issue notice to brothers for partition of the said property.

Followed by filing suit for partition.

Dear

In this case your mother should file a partition suit against her brothers.

In the suit she should also pray for temporary injunction(Stay) over the disputed land till disposal of the suit. 

After partition the property will be divided among your mother and her brothers equally. 

brother has no right to sell the said property without consent your mother . you can stop the said sale to third party by filing civil suit for permanent injunction for not to alienate to anybody before jurisdictional civil court.

Your mother can file a partition suit seeking her legitimate share in the proeprty that belonged to her father and also file an application for injunction seeking to restrain the defendants from alienating or encumbering the property in any manner till the disposal of the main partition suit.

you may discuss with a local advocate and file a partition suit immediately as suggested.